The present invention relates to an impact type dot printer and, more particularly, to a novel impact type dot printer capable of forming letters, numerals, symbols, pictures, graphs and so forth at a high speed by means of a single printing element.
The impact type dot printer has various advantages. Namely, it is possible to form letters, graphs and so forth at a high printing speed. In addition, printing can be made on a multiplicity of papers by the use of non-carbon copying papers. The most commonly used impact type dot printer is the wire printer which has 7 (seven) or more printing wires the ends of which are arrayed in a row in the direction of feed of the paper. This wire printer, however, has a complicated construction and requires a large number of parts. In addition, the weight of the printing head is considerably large, and a scanning mechanism and circuit power source matching such a heavy head is required.
Another known impact type dot printer is the helical platen type dot printer which may seem to resemble the dot printer of the present invention. This helical platen type printer incorporates a platen (rotary drum) having one or more helical projections formed on the peripheral surface thereof, and a cross bar hammer disposed to oppose the platen along the length of the latter so as to strike the projections. In this helical platen type dot printer, the cross bar hammer is formed linearly to extend along the axis of the platen and is adapted to strike the helical projections without being scanned in the direction perpendicular to the direction of feed of the recording paper. Therefore, for forming a letter constituted by a dot matrix of 7 rows and 5 columns, for instance, 7 increments of paper feed are necessary for each character row. Thus, the printing speed is impractically low. In addition, since the position of collision (intersection) between the cross bar hammer and the helical projections of the platen moves progressively in the lateral direction as the platen rotates, the cross bar hammer makes an innegligibly large twisting distortion when it collides with the helical projection on the end portion of the platen. As a consequence, the operation is rendered unstable. In addition, there is a practical limit in the length of the cross bar hammer, i.e. the number of characters which can be printed by a sole cross bar hammer. For increasing the number of characters per line, it is necessary to incorporate a plurality of cross bar hammers.